Energy coupling devices, motor vehicles with energy coupling devices as well as methods for their operation are extensively known in the prior art. They serve particularly for electrical coupling of electrical energy distribution networks such as the high-voltage on-board electrical system and the low-voltage on-board electrical system. In the present case, the focus is on d.c. voltage power distribution networks, wherein an electrical energy accumulator such as a type of battery is connected to at least one of the energy distribution networks. If the battery is a component of the high-voltage on-board electrical system, it is also known as a high-voltage battery.
Electrical energy distribution networks as well as the batteries for them find not only stationary applications, such as, for example, in uninterruptible power supply devices, electrical power supply devices in island operation, and/or similar instances, but also use in motor vehicles, and especially in electrically drivable motor vehicles, such as electric vehicles, hybrid vehicles, and the like.
Both the high-voltage on-board electrical system and the low-voltage on-board electrical system serve for the distributing of electrical energy between electrical units hooked up to the respective on-board electrical system, especially in a motor vehicle. Such electrical units may comprise, in addition to an electrical energy accumulator, such as the high-voltage battery of the high-voltage on-board electrical system or the like, electrical consumers, and/or the like, also an electrical energy source, such as a generator, a fuel cell, and/or the like, and also an electric drive mechanism, especially in the case of electrically drivable vehicles, which serves for the driving of the electrically drivable motor vehicle. Furthermore, a number of other electrical units may be involved, such as a lighting unit, headlights of the motor vehicle, interior lighting of the motor vehicle, and/or the like, but also other functional units such as a car radio, a navigation apparatus, an electrically operated air conditioning compressor, and/or the like.
An energy coupling device of this kind is known for example from DE 10 2014 205 650 A1. This discloses a two-stage d.c. voltage converter with power scaling. For this purpose, a circuit arrangement is provided at the high voltage side, comprising a plurality of parallel-connected boost-buck controllers. By means of the circuit arrangement at the high voltage side, a voltage matching from a high voltage side to a medium d.c. voltage is produced. By means of the circuit arrangement at the high voltage side, the medium d.c. voltage is held at a constant value. A circuit arrangement at the low voltage side is connected to the medium d.c. voltage, providing an electrical coupling of the medium d.c. voltage to a d.c. voltage at the low voltage side. The circuit arrangement at the low voltage side works with a fixed clock frequency at a working point having substantially a fixed transmission ratio.
Furthermore, DE 10 2009 046 501 A1 discloses a battery system with DC/DC converters. DE 10 2014 205 652 A1 moreover discloses a modulation method for a booster operation of a push-pull converter and DE 198 29 777 A1 discloses a DC/DC converter.
Even though the prior art has proven itself, there continues to be a need for improvement. Namely, it has been shown that the use of high-voltage batteries is undergoing constant development, especially improvement. In this way, it becomes possible to use high-voltage batteries also in fields which were heretofore reserved for other battery technologies, such as those based on lead acid batteries or the like. In particular, it is desirable to replace battery technologies with little future prospect, such as the lead acid battery or the like, with new technologies, such as those based on lithium ion technology or the like. The teaching of DE 10 2014 205 650 A1 proves to be a drawback here, since only slight efficiencies can be achieved especially in the partial load range. Yet the partial load range has proven to be a frequent operating condition. Also for this reason, neither has the teaching of DE 10 2014 205 650 A1 become widespread.